va 2.01,
Results of machine computations have been plotted graphically to
permit evaluation of the ratios of Eq. 17-23 for a range of slab
thicknessec and exposure point locations. These graphs are given
in Ref.54 for the five (5) pseudospectrum energies, along with the ratios
that permit conversion of circular to equivalent rectangular silsbe.
To illustrate the results of ehielding calculations from airborne
activity, Figs. 17-12 to 17-15
Ref.55)
ere included.
(reproductions of Figs. 7 to 10 of
The shielding factor is plotted vs total deck-
plating thickness for a number of locations within USS RANGER (CVA-61).
The monoenergetic calculations have been weighted in accordance with
the pseudospectra for unfractionated U-235 fission products at 70 sec
and 1.12 hr after fission.
Two sets of calculations wer» made for each
time, one set using only the nominal plating thicknesses (t}) to give a
minimal estimate of the shielding, and the other set using twice the
plating thicknesses (2t) to give expected shielding factor values. As
indicated in Ref.55, for airborne activity a considerable portion of
the incident radiation penetrates through the side of the ship rather
than through the weather deck. Therefore, the correlation of shielding
factor with total plating thickness overhead is not an accurate measure
of the radiation attenuation.
However, it represents the best yardstick
currently available.
17.5.6 Effect of Geometry at Unshielded Locations
No data are available either from water-surface bursts or the
earlier underwater bursts to establish experimentally the effect of the
geometry of the ship or of the aerosol on transit-radiation levels at
unshielded locations.
However, analysis? of shipboard data from the
Hardtack shots “indicates that the ship's superstructure has e detectable influence on the total gamma dose.... Because of the paucity
of GITR data, the analysis was based on doses registered on film packs"
(fixed at various locations in the ship). Furthermore, "the gamma records resulting from the passage of airborne radioactive material are
sufficiently characteristic that records from shots Wahoo and Umbrella
can usually be distinguished by inspection, particularly at downwind
location.” ‘The differences in the records are due to differences in
the geometries of the base surges resulting from the two shots.
Film packs were located at various frame mumbers, on both sides of
the ships (toward and away from surface zero).
According to Ref. 32,
plots of film-pack doses vs frame number, for both shots, show a
fairly consistent difference between film pack doses on the opposite
sides of the closer ships, a difference coneistent with the attitude
of the ship. In general, film packs on the side of the ship toward
surface zero registered significantly higher doses than those on the
side away from surface zero.
In addition, the same plots give a char-
acteristic curve shape for each ship, regardless of the ship's attitude
BEST AVAILABLE COPY
17-62
Ser erence me ee rn ones =
ne mere ey ees ee eee ee eee
ee ee ee ee +ee eee we ee
eee